How to make an effective Magnetorheological Fluid?

I want to know how to make a Magnetorheological Fluid for a science project. I have decided to use Oleic Acid as the surfactant but I do not know what "particles" I should use. Will Iron Fillings be effective? Or should I find some other material that will be more effective?

I have researched this for my own project, and it seems that super-fine iron particles called "Carbonyl iron powder" are used frequently. I still haven't found a place to from which to buy this other than online, but that's my two cents.